Field of the invention
This invention relates to a method of, and apparatus for, detecting the presence of contaminants in liquids. The invention has been developed particularly in relation to the detection of contaminants such as water or paraffin in oil which is used in a quenching process for effecting cooling of a work piece, at a controlled rate, from a relatively high temperature by immersion of the work piece in the oil. It will however be appreciated that the invention will find application generally, for example in detection of contamination of lubricating or hydraulic oils.
If oil used for quenching should become contaminated, some extremely disadvantageous and undesirable effects may arise. Firstly, the presence of even a relatively small proportion of water has a great effect, as will hereafter be described in more detail, on the rate and evenness of cooling of a hot work piece immersed therein. This can give rise to the formation of quench cracks in the work piece. In addition to this, quantities of water in quenching oil may, if they come into contact with a hot work piece or if the general temperature in the mass of quenching oil should rise sufficiently high, be vaporised into steam with extreme rapidity which may cause foaming of the oil or even the explosive ejection of oil from the tank or bath in which the operation is taking place. The presence of paraffin in quenching oil is even more undesirable, because of the fire hazard.
Water may be present in quenching oil baths due to condensation effects, or due to leakage of pipes or valves which may, for example, form part of a cooling system for the oil. If there is no agitation of the oil, water would merely remain at the bottom of the tank or bath, but if the oil is subjected to any circulation system (which in practice is very frequently encountered) the water may remain in suspension in the form of droplets in the oil. This effect is aggravated if the oil is washable or contains an emulsifying agent.
It has been proposed hitherto to detect the presence of water in quenching oil by methods involving the abstraction of a sample of the oil, either from a bath or from a circulation system for the oil, and heating of the oil sample to a temperature at which any water therein would vaporise. The vapour pressure of the sample would then rise above that normally to be expected if the oil were pure, and this rise in pressure can then be detected. Such methods, however, have disadvantages in that they tend to be sensitive mainly to the presence of water alone, and are not so sensitive to the presence of other contaminants. Further, problems of adequate or even undue sensitivity can arise with this type of apparatus, and further difficulties with durability of the various components thereof.